1. Field of the Invention
The present invention relates to elevator drive machines and more specifically to an elevator drive machine having a rotating traction sheave between rotors of multiple motors along the axis of rotation.
2. Description of the Background Art
The drive machine of a traction sheave elevator has a traction sheave with grooves for the hoisting ropes of the elevator and an electric motor driving the traction sheave either directly or via a transmission. Traditionally the electric motor used to drive an elevator has been a d.c. motor, but increasingly a.c. motors, such as squirrel-cage motors with electronic control are being used. One of the problems encountered in gearless elevator machines of conventional construction has been their large size and weight. Such motors take up considerable space and are difficult to transport to the site and to install. In elevator groups consisting of large elevators, it has sometimes even been necessary to install the hoisting machines of adjacent elevators on different floors to provide enough room for them above the elevator shafts placed side by side. In large elevator machines, transmitting the torque from the drive motor to the traction sheave can be a problem. For example, large gearless elevators with a conventional drive shaft between the electric motor and the traction sheave are particularly susceptible to develop significant torsional vibrations due to torsion of the shaft.
Recently, solutions have been presented in which the elevator motor is a synchronous motor, especially a synchronous motor with permanent magnets. For example, the specification of WO 95/00432 presents a synchronous motor with permanent magnets which has an axial air gap and in which the traction sheave is directly connected to a disc forming the rotor. Such a solution is advantageous in elevator drives with a relatively low torque requirement, e.g. a hoisting load of about 1000 kg, and in which the elevator speed is of the order of 1 m/s. Such a machine provides a special advantage in applications designed to minimize the space required for the elevator drive machine, e.g. in elevator solutions with no machine room.
The specification of FI 93340 presents a solution in which the traction sheave is divided into two parts placed on opposite sides of the rotor in the direction of its axis of rotation. Placed on both sides of the rotor are also stator parts shaped in the form of a ring-like sector, separated from the rotor by air gaps.
In the machine presented in the specification of FI 95687, the rotor and the stator parts on either side of it with an air gap in between are located inside the traction sheave. In this way, the traction sheave is integrated with the rotor, which is provided with magnetizing elements corresponding to each rotor part.
The specification of DE 2115490 A presents a solution designed to drive a cable or rope drum or the like. This solution uses separate linear motor units acting on the rim of the drum flanges.
For elevators designed for loads of several thousand kg and speeds of several meters per second, none of the solutions presented in the above-mentioned specifications are capable of developing a sufficient torque and speed of rotation. Further, problems might be encountered in the control of axial forces. In motors with multiple air gaps, further difficulties result from the divergent electrical and functional properties of the air gaps.
This imposes special requirements on the electric drive of the motor to allow full-scale utilization of the motor. Special requirements generally result in a complicated system or a high price, or both.
The specification of GB 2116512 A presents a geared elevator machine which has several relatively small electric motors driving a single traction sheave. In this way a machine is achieved that needs only a relatively small floor area. The machine presented in GB 2116512 A can be accommodated in a machine room space not larger than the cross-sectional area of the elevator shaft below it. Such an advantageous machine room solution has not been usable in the case of large gearless elevators because these typically have a machine with one large motor that extends a long way sideways from the traction sheave. The specification of EP 565 893 A2 presents a gearless elevator machine comprising more than one modular motor unit, which are connected together to drive traction sheaves also connected together. In such a solution, the length of the machine increases as its capacity is increased by adding a motor module. The problem in this case is that the length of the machine is increased on one side of the traction sheave, which is why the machine extends beyond the width of the elevator shaft below. Supporting and stiffening such a long machine so that its own weight and the rope suspension will not produce harmful deformations is likely to result in expensive and difficult solutions. For instance, the bending of a long machine requires a special and expensive bearing solution. If bending or other forms of load produce even the slightest flattening of the traction sheave to an elliptical shape, this will probably lead to vibrations that reduce the travelling comfort provided by the elevator.